1. Field of the Invention
This invention relates to a dimethyl ether reforming catalyst, particularly, a dimethyl ether reforming catalyst for reforming dimethyl ether used as a raw material of fuel gas of a fuel cell, and to a fuel cell device using the dimethyl ether reforming catalyst.
2. Description of the Prior Art
In general, a polymer electrolyte fuel cell in which an anode and a cathode are arranged at both sides of a proton-conductive polymer electrolyte membrane is known as a fuel cell. In the polymer electrolyte fuel cell, fuel gas mainly including hydrogen is supplied to the anode and oxidation gas such as air is supplied to the cathode, whereby the electrochemical reaction is generated to shift proton in the polymer electrolyte membrane, to thereby produce electromotive force. This polymer electrolyte fuel cell is known as an energy-efficient fuel cell that can convert chemical energy of the fuel gas to electrical energy directly.
It is well known that in this polymer electrolyte fuel cell, for example methanol, which is used as a raw material of the fuel gas, is brought into contact with steam so that it can be reformed to produce the fuel gas to be supplied to the anode. Typically, a Cuxe2x80x94Zn catalyst is widely used for such a reform of methanol.
In addition to methanol, various raw materials, such as natural gases, are being proposed as the raw material of the fuel gas. Among others, dimethyl ether, which is easily liquefied when pressurized to several atmospheres (e.g. 5 atmosphere) at room temperature or when reduced to very low temperature (e.g. xe2x88x9225xc2x0 C.), is in hopes of use in terms of conveyance, storage and easiness to handle.
However, even when dimethyl ether is brought into contact with steam, for example, in the presence of the Cuxe2x80x94Zn catalyst so that it can be reformed to produce hydrogen, the concentration of hydrogen in the mixed gas obtained by that reform is low and such is not of practical.
European patent bulletin (EP-A-754649) describes the method that dimethyl ether is allowed to react with steam by the following formulas in the presence of a catalyst obtained by solid acid and a methanol decomposing catalyst being physically mixed, to thereby produce a mixed gas rich in hydrogen.
CH3OCH3+H2Oxe2x86x922CH3OHxe2x80x83xe2x80x83(1)
CH3OH+H2Oxe2x86x923H2+CO2xe2x80x83xe2x80x83(2)
However, the concentration of hydrogen in the mixed gas obtained by this method is still insufficient. Accordingly, a mixed gas of higher concentration of hydrogen is being desired for use as a fuel gas of a fuel cell.
It is the object of the present invention to provide a dimethyl ether reforming catalyst that can reform dimethyl ether to produce a mixed gas of higher concentration of hydrogen. Also, it is the object of the present invention to provide a fuel cell device using the dimethyl ether reforming catalyst.
The present invention is directed to a novel dimethyl ether reforming catalyst wherein copper, or copper and at least one transition metal except the copper is supported on a solid acid.
It is preferable that the solid acid is at least one material selected from by the group consisting of activated alumina, silica-alumina and zeolite. Preferably, an amount of supported copper, or an amount of supported copper and at least one transition metal except the copper, to the solid acid is 4-20 weight %.
It is preferable that the dimethyl ether reforming catalyst is produced by the copper, or the copper and the at least one transition metal except the copper being supported on the solid acid molded to have a predetermined size. Preferably, the solid acid is molded into a fine form. Further preferably, the solid acid is molded into a pellet form having a diametral length of 3.5 mm or less or a granular form having a particle size of 2 mm or less.
Also, it is also preferable that the dimethyl ether reforming catalyst is produced by the copper, or the copper and the at least transition metal except the copper being supported on the solid acid and then being pulverized. Preferably, the dimethyl ether reforming catalyst is pulverized into a fine form. Particularly, the dimethyl ether reforming catalyst is preferably pulverized to have a particle size of 2 mm or less.
Further, it is also preferable that the dimethyl ether reforming catalyst further comprises a solid strong acid. Preferably, the solid strong acid is solidified phosphoric acid and/or heteropoly acid. Also, it is preferable that the solid acid on which the copper, or the copper and the at least one transition metal except the copper is supported and the solid strong acid have a fine form. Particularly, the solid acid on which the copper, or the copper and the at least one transition metal except the copper is supported and the solid strong acid have a particle size of 2 mm or less. Further, it is preferable that the solid acid on which the copper, or the copper and the at least one transition metal except the copper is supported and the solid strong acid are in volume ratios in the range of 1:3 to 3:1.
The present invention includes a fuel cell device comprising (i) a reforming device using a dimethyl ether catalyst in which copper, or copper and at least one transition metal except the copper is supported on a solid acid, to reform dimethyl ether and thereby produce a mixed gas and (ii) a fuel cell to which the mixed gas is fed as a fuel gas.